The present invention relates to data center infrastructure, and more particularly, this invention relates to credit-based link level flow control and credit exchange using Data Center Bridging eXchange (DCBX).
Ethernet port-based flow control is based on a reactive stop-and-go (on-off) mechanism, called PAUSE, as defined in Institute of Electrical and Electronics Engineers (IEEE) standard 802.3x, which is used only after a receiver's buffer backlog exceeds a certain high watermark, sending a PAUSE (i.e., stop) signal to the sender, and sending an UNPAUSE (i.e., go) signal when the receiver's buffer backdrop drops below a low watermark. To ensure that no frame drops caused by buffer overflow(s) occur, the receiver's high watermark must be set at least one bandwidth-delay product (BDP) below the receiver's buffer capacity, thus increasing buffer size requirements. Moreover, for a given threshold setting, an increase in BDP, e.g., due to installing a longer cable between the sender and the receiver, or due to delayed processing of a PAUSE frame, may lead to unwanted frame drops. These issues are exacerbated by continuously increasing line rates (from the original 10 Mb/s per port up to 100 Gb/s and faster) which leads to increasing BDP. Accordingly, it would be beneficial for Ethernet to adopt proactive reservation-based flow control and frame acceptance schemes with a mechanism to guarantee buffer space at the receiver to ensure absence of frame drops independent of BDP.
Interaction between peer ports before data exchange brings in more certainty and better resource utilization. Ethernet does not have such a mechanism for the purpose of catering to specific applications and convergence of Infiniband over Ethernet.
Therefore, Ethernet installations would benefit greatly from a credit-based flow control mechanism to bring in more certainty for transmission.